Cellulose acetate-ammonium nitrate propellant containing a quaternary ammonium salt of a hexacyclic ureide



United States Patent CELLULOSE ACETATE-AMMONIUM NITRATE PROIELLANT CONTAINING A QUATER- NARY AMMONIUM SALT OF A HEXACY- CLIC UREIDE Lionel A. Henderson, Columbus, Ind., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana N0 Drawing. Filed Aug. 7, 1964, Ser. No. 388,274

Claims. (Cl. 149-18) This invention relates to ammonium nitrate propellant compositions which contain an ash-free catalyst for promoting the combustion of the ammonium nitrate.

In ammonium nitrate propellant compositions which mainly comprise ammonium nitrate particles and an oxidizable organic binder material, which permits the shaping of the composition into a definite configuration or grain, it is nesessary to promote the combustion of the composition by the use of a catalyst. Commonly used catalysts in the past have been metallic compounds such as ammonium dichromate, the Prussian blues and sodium salts of some organic acids. However, the past history of the use of propellants catalyzed by the above compounds has shown that the resulting gases are detrimental to the hardware in use, such as nozzles of a rocket motor, due to the build-up of deposits and to the erosion caused by metallic compounds, such as sodium carbonate, from the catalyst in the gas streams. For many purposes, particularly in gas generator systems with close tolerances and in turbine power sources where essentially solid-free gases having a low order of erosion are required, there has been a need for an effective ashless organic catalyst for ammonium nitrate propellant compositions.

I have discovered that the quaternary ammonium salts of hexacyclic ureides, such as the tetramethyl ammonium salt of barbituric acid, function as effective combustion catalysts for ammonium nitrate propellant compositions and that the use of these catalysts greatly reduce the above problems encountered with metallic catalysts. These salts are considered unusual because I have found that quaternary ammonium salts of other acids, e.g., picric acid, and another salt of barbituric acid, the guanidine salt, do not function as satisfactory combustion catalysts.

Briefly, the invention is directed to an ammonium nitrate propellant composition which includes a small catalytic amount of the quaternary ammonium salt of a hexacyclic ureide. The propellant composition comprises ammonium nitrate as the major component and between about 10 and 40 weight percent of an oxidizable organic binder material.

The ammonium nitrate may be the high purity material commonly produced by synthetic plants today, or it may be a technical grade containing small amounts of inorganic impurities. In addition to the ammonium nitrate, for special purposes, small amounts of sodium nitrate or potassium nitrate may be present. The decomposition rate of the ammonium nitrate is influenced by the particle size. For gas generation purposes, the ammonium nitrate is finely divided. Particularly suitable ammonium nitrate will contain about 80 weight percent of material having a screen size greater than 80 mesh and smaller than 30 mesh. The more finely powdered ammonium nitrate is used where higher burning rates are desired. Generally the propellant composition will contain between about 60 and about 80% (and commonly about 62-73%) of ammonium nitrate. In all cases, the major component present in the composition in ammonium nitrate.

In order to permit the shaping of the ammonium nitrate composition into definite configurations, a matrix former or binder material is present. When ammonium nitrate decomposes, freeoxygen is released. The existence of this free-oxygen oxidizable organic materals to be used as the binders and thereby obtain additional gas production. These oxidizable organic materials may contain only carbon and hydrogen, for example, high molecular weight hydrocarbons such as asphalts or resid uums, and rubbers, either natural or synthetic. Or, it may contain other elements in addition to carbon and hydrogen, for example, as in Thiokol rubber and neoprene. The stoichi-ome'tr'y' of thcomposition is improved, with respect to smoke production, by the use of organic materials containing combined oxygen as the binder-s. The binder or matrix former may be a single compound such as a rubber or asphalt or it may be .a mixture of compounds. The mixtures are particularly suitable when special characteristics are to be imparted to the propellant which can not be obtained by the use of a single compound.

Multi-component binder, or matrix former, consists of a polymeric base material and a plasticizer therefor. Particularly suitable polymeric base materials are cellulose esters of alkanoic acids containing from 2 to 4 carbon atoms such as cellulose acetate, cellulose acetate butyrate and cellulose propionate. The polyvinyl resins such as polyvinylchloride and polyvinyl acetate are good bases. Styreneacrylonitrile is an example of a copolymer which forms a good base material. Polyacrylonitrile is another suitable base material.

The plasticizer component of the binder also, preferably, contains combined oxygen. The oxygen may be present in the plasticizer as an ether linkage and/or hydroxyl and/ or carboxyl; also the oxygen may be present as a part of an inorganic substituent, particularly, a nitro group. In general, any plasticizer which is adapted to plasticize the particular polymer may be used in the invention. A single plasticizing compound may be used; more usually two or more compounds are used in conjunction. Exemplary classes of plasticizers which are suitable are set out below. (It is to be understood that these classes are illustrative only and do not limit the types of organic compounds which may be used to plasticize the polymer.)

Di-lower alkyl-phthalates, e.g., dimethyl phthalate, dibutyl phthalate, dioctyl phthalate and dimethyl nitrophthalate.

Nitrobenzenes, e.g., nitrobenzene, dinitrobenzene, nitrotoluene, dinitrotoluene, nitroxylene, and nitrodiphenyl.

Nitrodiphenyl ethers, e.g., nitrodiphenyl ether and 2,4-dinitrodiphenyl ether.

Tri-loweralkyl-citrates, e.g., triethyl citrate, tributyl citrate and triamyl citrate.

Acyl tri-lower alkyl-citrates where the acyl group contains 2-4 carbon atoms, e.g., acetyl triethyl citrate and acetyl tributyl citrate.

Glycerol-lower alkanoates, e.g., monoacetin, triacetin,

glycerol tripropionate and glycerol tributyrate.

Lower alkylene-glycol-lower alkanoates wherein the glycol portion has a molecular weight below about 200, e.g., ethylene glycol diacetate, triethylene glycol dihexoate, triethylene glycol dioctoate, polyethylene glycol dioctoate, dipropylene glycol diacetate, nitromethyl propanediol diacetate, hydroxyethyl acetate and hydroxy propyl acetate (propylene glycol monoacetate).

Dinitrophenyl-lower alkyl-lower alkanoates, e.g., dinitrophenyl ethylacetate, and dinitrophenyl amyloctoate.

Lower alkylene-glycols wherein the molecular weight is below about 200, e.g., diethylene glycol, polyethylene glycol (200), and tetrapropylene glycol.

Lower alkylene-glycol oxalates, e. g., diethylene glycol oxalate and polyethylene glycol (200) oxalate.

Lower alkylene-glycol imaleates, e. g., ethylene glycol maleate and bis-(diethylene glycol monoethyl ether) maleate.

Lower alkylene-glycol diglycolates, e.g., ethylene glycol diglycolate and diethylene glycol diglycolate.

Miscellaneous diglycolates, e.g., dibutyl diglycolate, di-

methylalkyl diglycolate and methylcarbitol diglycolate.

Lower alkyl-phthalyl-lower alkyl-glycolate, e.g., methyl phthalyl ethyl glycolate, ethyl phthalyl ethyl glycolate and butyl phthalyl butyl glycolate.

Di-lower alkyloxy-tetraglycol, e.g., dimethoxy tetra glycol and dibuto-xy tetra glycol.

Nitrophenylether of lower alkylene glycols, e.g., dinitrophenyl ether of triethylene glycol and nitrophenyl ether of polypropylene glycol.

Nitrophenoxy alkanols wherein the alkanol portion is derived from a glycol having a molecular weight of not more than about 200. These may be pure compounds or admixed with major component bis(nitrophenoxy) alkane.

The catalyst of this invention is the quaternary ammonium salt of a hexacyclic ureide. Cyclic uredies are described on pages 244-245 of Organic Chemistry by Fieser and Fieser, third edition, copyright 1956. Particular hexacyclic ureides useful for the purposes of this invention have 23 nitrogen atoms in the ring and, in their enol form, have 2-3 hydroxy substituted carbon atoms in the ring. Advantageously, the hexacyclic ureides contain only carbon, nitrogen, oxygen and hydrogen. Particularly advantageous ureides are barbituric acid, cyanuric acid, uracil, and uric acid,

The quaternary ammonium portion of the defined catalyst has the formula:

where one or more of the R groups is alkyl, aryl or combinations of these groups. Particularly useful are the tetra-lower alkyl quaternary ammonium salts, and aryl tri-lower alkyl quaternary ammonium salts, and diaryl di-lower alkyl quaternary ammonium salts. Lower alkyl refers to groups containing up to about 6 carbon atoms. Examples of useful alkyl groups are methyl, ethyl, propyl, hexyl, and the like and of useful aryl groups are benzyl, tolulyl, naphthyl, diphenyl and the like.

The catalytic quaternary ammonium salts are prepared by neutralizing the acids with a stoichiometric amount of the quaternary ammonium hydroxide. The amount of the hydroxide used is based on the neutralization of one acidic hydrogen of the acid.

Normally only a small amount of the catalyst is required in the ammonium nitrate propellant composition to provide the required catalytic effect. Generally the small amount is between about 0.1-15 weight percent of the propellant composition.

In addition to the main components, i.e., ammonium nitrate, binder and catalyst, the propellant composition may contain other components. A promoter to enhance the activity of the catalyst may be utilized. Commonly this a a carbon component of the type described on pages 34 of copending application S.N, 219,735, filed August 27, 1962 which pages are incorporated into and made a part of this specification by reference. The preferred carbons are the highly adsorptive activated carbons and the carbon blacks described in the above reference.

In addition, materials may be present to improve low temperature, ignitability, for instance, oximes or asphalt; and surfactants may be present in order to improve the adhesion of the nitrate and the binder and also to improve the shape retention characteristics of the composition.

Also, aromatic hydrocarbon amines may be present in order to improve the storage stability, particularly at higher temperatures, of the ammonium nitrate propellant composition. Illustrations of these aromatic amines are toluene diamine, diphenyl amine, naphthalene diamine, and toluene triamine. In general, these are present in an amount between about 0.5 and 5 percent. Better stabilization is obtained with a combination of the aromatic amines and N-phenylmorpholine and N-alkyl propylene diamines where the alkyl group contains about 12-22 carbon atoms. These diamines are available from the Armour Chemical Division, Armour and Company. A particularly useful diamine is one identified as Duomeen-T which means that the alkyl group is derived from tallow fatty acids. In general, when aromatic hydrocarbon amines are also present, between about 0.1% and 1% of N-phenylmorpholine and/or the N-alkyl propylene diamine will be present.

An illustrative ammonium nitrate propellant composition which provides particularly good properties comprises about 62 to 73% of ammonium nitrate, about 6 to about 14 weight percent of cellulose acetate, about 6 to 14 weight percent of acetyltriethylcitrate, about 5 to about 13 weight percent of dinitrophenoxyethanol, about 0.2 to 3.0 weight percent of toluene diamine, about 0.5 to 7.0 weight percent of carbon, and about 0.5 to 15 weight percent of a quaternary ammonium salt of barbituric acid, cyanuric acid, uracil, or uric acid.

The present invention will be better understood by reference to the following examples which illustrate the beneficial effects of the invention. It is to be understood that the following example are given for the purpose of illustration only and do not serve in any way to limit the scope of the present invention.

Example I A propellant composition was prepared from the following components in the following approximate weight percentages:

Formulation:

Cellulose acetate 10.30

Acetyltriethylcitrate 10.30 Dinitrophenoxyethanol 9.40 Toluene diamine 1.00 Ammonium nitrate 65.00 Texas E carbon 2.00 Tetramethyl ammonium barbiturate 2.00

A one-quart batch of the composition was prepared by mixing the above components for about one hour in a laboratory mixer. The mixing temperature was about C. Two plasticizers were used for the cellulose acetate binder. These plasticizers were acetyltriethylcitrate and dinitrophenoxyethanol.

After mixing, the resulting pasty mass was compression molded into a slab approximately /2" in thickness. The slab was subsequently sawed into strips for the burning rate test which was conducted in the Crawford Bomb pressurized at 1000 p.s.i.a. and at 70 F. In addition to obtaining the burning rate, the pressure exponent n was obtained. The pressure exponent is the numerical value equal to the slope of the curve of burning rate in inches per second obtained by plotting the burning rate versus pressure on log-log paper. The temperature coefficient at constant pressure, up, was also obtained for the composition.

The results of the above tests are shown below in comparison with those for a similar composition having a metallic catalyst, sodium barbiturate, in place of the tetramethyl ammonium barbiturate.

TABLE I TABLE II Catalyst 1 +70 11 1 +170 1' -05 up Catalyst Weight, 11 R at 70 F.

percent Sodium Barb 0. 0840 0. 04 0.0920 0.0650 0.15 5

'letramcthyl A1mn.Barb .0555 0.66 .0010 .0445 0.13 BZTMA 3 0.08 .0030

BZIMA Barbiturate. 3 0.00 .0068

' TMA Picrate 3 Failed.

The above results demonstrate that the composition 7 g catalyzed by the tetramethyl ammonium barbiturate exhib- %;,1g g 8: 18328 ited good propellant properties in comparison to those of the composition catalyzed by sodium barbiturate. The pressure exponents and the temperature coeflicients for both compositions were very similar with the temperature coefiicient of the first composition being slightly higher to that of the second.

Strands from the composition catalyzed by the tetramethyl ammonium barbiturate Were aged for four successive 24-hour periods at 170 F. and show no change in burning rate. Propellants containing sodium barbiturate generally have shown an increase in burning rate.

Example II A propellant composition was prepared from the following components in the following approximate weight percentages:

Chemical: Percent Cellulose acetate 10.32 Acetyltriethylcitrate 10.30 Dinitrophenoxyethanol 9.40 Texas E carbon 1.40 Toluene diarnine 0.80 N-phenylmorpholine 0.20 Graphite 0.05 Duomeen-T 0.20

Norite carbon 2.20

Ammonium nitrate 62.73 Benzyltrimethyl ammonium barbiturate 2.00

1 As shredded binder.

The composition was prepared in essentially the same manner as that described in Example 1, except that -quart batches were made.

Motor firings were carried out on the above propellant composition. In these tests, it was determined that there was no build-up or formation of ash on the nozzle of the motor and no residue remaining in the motor case, indicating a propellant having clean burning characteristics.

Example 111 Tests were also carried out on propellant compositions catalyzed with the quaternary ammonium salts listed in Table II below. The propellant formulation used in these tests was:

Chemical: Percent Cellulose acetate 10 Acetyltriethylcitrate 9 Dinitrophenoxyethanol 10 Texas E carbon 3 Toluene diamine 1 Ammonium oxalate 0.4 Ammonium nitrate 63.6 Catalyst 3.0

The results of the test are listed in Table II, below, opposite the identification of each catalyst.

The above results show that the quaternary ammonium salts of cyanuric acid, barbituric acid, and uric acid are effective composition catalysts for ammonium nitrate propellant compositions. The results also demonstrate that the above quaternary salts of picric acid were not significantly effective as composition catalyst.

Having thus described the invention, what is claimed is:

1. An ammonium nitrate propellant composition comprising ammonium nitrate as the major component, between about 10 and 40 weight percent of an oxidizable organic binder material, and a small catalytic amount of a quaternary ammonium salt of a hexacyclic ureide, said ureide having 2-3 nitrogen atoms in the ring and in its enol form having 23 hydroxy substituted carbon atoms in the ring.

2. The ammonium nitrate propellant composition of claim 1 wherein said ureide is barbituric acid.

3. The ammonium nitrate propellant composition of claim 1 wherein said ureide is cyanuric acid.

4. The ammonium nitrate propellant composition of claim 1 wherein said ureide is uracil.

5. The ammonium nitrate propellant composition of claim 1 wherein said ureide is uric acid.

6. The ammonium nitrate propellant composition of claim 2 wherein said quaternary ammonium salt is a tetramethyl ammonium salt.

7. The ammonium nitrate propellant composition of claim 2 wherein said quaternary ammonium salt is a benzyltrimethyl ammonium salt.

8. The ammonium nitrate propellant composition of claim 1 wherein said small amount is between about 01-15 weight percent.

9. The ammonium nitrate propellant composition of claim 8 wherein said composition includes a promoter for said catalyst.

10. An ammonium nitrate propellant composition comprising ammonium nitrate as the major component, about 6 to 14 weight percent of cellulose acetate, about 6 to 14 weight percent of acetyltriethylcitrate, about 5 to about 13 weight percent of dinitrophenoxy ethanol, about 0.2 to 3.0 weight percent of toluene diamine, about 0.5 to 7.0 weight percent of carbon, and about 0.5 to 10 weight percent of a quaternary ammonium salt of a hexacyclic ureide, said ureide having 2-3 nitrogen atoms in the ring and in its enol form having 2-3 hydroxy substituted carbon atoms in the ring.

References Cited by the Examiner UNITED STATES PATENTS 3,148,096 9/1964 Butcher 149-19 3,161,550 12/1964 Mosher et a1. 14919 3,180,772 4/1965 OConnor 149-47 BENJAMIN R. PADGETT, Primary Examiner.

LEON D. ROSDOL, Examiner. 

1. AN AMMONIUM NITRATE PROPELLANT COMPOSITION COMPRISING AMMONIUM NITRATE AS THE MAJOR COMPONENT, BETWEEN ABOUT 10 AND 40 WEIGHT PERCENT OF AN OXIDIZABLE ORGANIC BINDER MATERIAL, AND A SMALL CATALYTIC AMOUNT OF A QUATERNARY AMMONIUM SALT OF HEXACYCLIC UREIDE, SAID UREIDE HAVING 2-3 NITROGEN ATOMS IN THE RING AND IN ITS ENOL FORM HAVING 2-3 HYDROXY SUBSTITUTED CARBON ATOMS IN THE RING. 